The approaches described in this section could be pursued, but are not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section. Furthermore, all embodiments are not necessarily intended to solve all or even any of the problems brought forward in this section.
Time division multiplex access (TDMA) wireless systems such as GSM transmit data in fixed-length timeslots, and a training sequence is included in the timeslot, which is designed to allow the receiver to detect timing information and to obtain channel coefficients through channel estimation for further channel equalization.
Eight training sequences for GSM normal bursts are defined in the 3GPP specification (see TS 45.002, “GERAN: Multiplexing and multiple access on the radio path”) and are used for burst synchronization and channel estimation in current GSM/EDGE Radio Access Network (GERAN) systems.
Voice services over Adaptive Multi-user channels on One Slot (VAMOS) is an ongoing work item in GERAN that aims at increasing voice capacity of the GERAN in the order of a factor of two per base station (BTS) transceiver both in the uplink and the downlink by multiplexing at least two users simultaneously on the same physical radio resource, i.e., multiple users share the same carrier frequency and the same timeslot.
VAMOS technology is a cost efficient way to handle increasing traffic growth, and can further help operators to make more efficient use of their GSM resources. The more efficient use of the GSM networks further means that less hardware is needed to support a given traffic hence helps to reduce energy consumption and related CO2 emissions.
VAMOS technology includes two phases. The first phase (VAMOS-1) comprises the introduction of new training sequences and requires an update of channel estimation in the mobile station (MS). The second phase (VAMOS-2) requires implementation, in the mobile station, of an advanced receiver mode or VAMOS-2 mode, in which the mobile station receiver is set to process VAMOS-2 communication.
A current solution consists to activate VAMOS-2 mode by default, or systematically when GSM network is informing the mobile station with binary flag that data are transmitted in VAMOS-2 mode. This solution is not providing good signal to noise ratio (SNR) performances.
EP 2 157 752 discloses a method for reducing the SNR degradation by using a training sequence selection. However, this method may fail to optimize the SNR in some GSM network configurations.
Embodiments of the invention will improve the situation.